Weeks of feverish media speculation over the arrival of the royal baby, Kate, 31, was taken shortly before 0500 GMT on Monday to the private wing of St Mary's Hospital in Paddington, west London, where William himself was born in 1982.

"The duchess travelled by car from Kensington Palace to the Lindo Wing at St Mary's Hospital with the Duke of Cambridge," Kensington Palace said in a statement.

"Things are progressing as normal. It wasn't an emergency."

Royal sources have said Kate has planned a natural birth with William, a Royal Air Force search and rescue helicopter pilot, to be at her side.

The sex of the baby, who will be third in line to the throne behind grandfather Prince Charles and father William, is unknown as the royal couple want it to be a surprise. Bookmakers have a girl as the firm favourite.

Newspapers have speculated Kate's sister Pippa and mother Carole Middleton might be present for the birth while Queen Elizabeth will be among the first to be informed of the arrival.

The baby will be delivered by Marcus Setchell, the queen's former gynaecologist.

Kate, who needed hospital treatment after suffering acute morning sickness in the early part of the pregnancy, made her last public appearance on June 15 at the "Trooping the Colour", a military ceremony to mark Queen Elizabeth's official birthday.

The BBC reported she entered the hospital though a back door and avoided the crowd of media from around the world who have camped outside the hospital since July 1.

The Lindo Wing, where maternity rooms cost from 5,000 pounds ($7,800) for a one-night stay, is where the late Princess Diana gave birth to William, 31, and to his younger brother Harry, who will drop a place in the line of succession after the arrival.